1. Field of the Invention
The invention relates to a roller bearing.
2. Description of Related Art
Roller bearings are used as bearings that support rotating shafts of various types of equipment. For example, in a hydraulic pump for a construction machine, a roller bearing is used to receive a component of an axial load imposed on a piston and a swash plate.
The roller bearing includes an inner ring, an outer ring, a plurality of rollers, and an annular cage that holds the rollers. The cage includes a pair of annular rings and a plurality of cage bars joining the annular rings together. Areas enclosed by the pair of annular rings and circumferentially adjacent cage bars are configured as pockets that hold respective rollers (see, for example, FIG. 1 in Japanese Patent Application Publication No. 2005-69282 (JP 2005-69282 A)). In recent years, resin has been adopted as a material for the cage in order to meet a demand for reduced costs.
In some cages, tabs 93 are provided in a radially outer area of a cage bar 92 so as to prevent a roller 99 from slipping out through a pocket 91 as depicted in FIG. 11. The tabs 93 protrude from the cage bar 92. When the bearing is assembled, the roller 99 in the pocket 91 comes into contact with inner surfaces 94 of the tabs 93. Thus, the roller 99 can be prevented from slipping out (falling) through the pocket 91. When assembly of the bearing is complete, the tabs 93 allow the cage 90 to be positioned between the inner ring and the outer ring by the rollers 99.
To allow the cage 90 as described above to be molded using resin, a molten resin is poured into a cavity in a mold and solidified. To allow the cage 90, which is a molded product, to be demolded, a part 98 of the mold that penetrates the cage 90 in a radial direction needs to be extracted through the molded pocket 91 toward the outside in the radial direction (arrow Y direction in FIG. 12) as depicted in FIG. 12.
At this time, what is called forced extraction needs to be performed in which the part 98 of the mold is extracted while the tabs 93 are being elastically deformed. In FIG. 12, directions in which the tabs 93 are elastically deformed are depicted by arrows K1 and K2. It is expected that, when forced extraction is performed in this manner, heavy loads are imposed on forcibly extracted portions (tabs 93) and peripheries thereof, leading to local stress. The stress may cause the cage 90, formed of the resin, to be subjected to whitening or damage such crack or breakage.